This invention relates generally to a servo system. More particularly, this invention relates to a numerical control apparatus for a mechanical hydraulic servo valve.
A conventional numerical control apparatus for slide mechanism generally includes a ball screw driven by a servo motor or stepping motor. A ball nut carries a slide element thereon and is engaged with the ball screw. The rotation of the ball screw can be converted into the rectilinear movement of the ball nut because of the engagement between the ball screw and the ball nut. This kind of numerical control apparatus suffers from the following disadvantages:
(1) Because a ball screw of a very high precision is needed, it is difficult to make and maintain such a ball screw, resulting in high manufacturing costs. In addition, if the slide element is bulky, a large-size ball screw would be needed, also increasing its manufacturing costs.
(2) When a large-size screw is used, it must be driven by a high horsepower stepping motor or servo motor and the one motor can serve one slide element only. Thus, manufacturing cost is increased further.
(3) Due to uneven load, partial travel, long term serving and sudden impact by error, uncurable irregular worn-out backlash often occurs between the ball screw and the ball nut even when the ball screw and the ball nut are of a high precision.